Sensors which are based on the correlation optical principle to determine movement are described in the referenced publications, and more specifically in "Journal of the Optical Society of America", Vol. 53, No. 12, December 1963, pp. 1416 to 1422, article by J. T. Ator, entitled "Image-Velocity Sensing with Parallel-Slit Reticles"; and "APPLIED OPTICS", Vol. 5, No. 8, August 1966, pp. 1325 to 1331, article by J. T. Ator, entitled "Image Velocity Sensing by Optical Correlation". The principle of movement sensing has been carried forward since these early investigations, and commercial structures made by the Leitz company of the Fed. Rep. Germany, and marketed under the trademarks "Correvit-L" and "Correvit-Q", are described in "F & M, Feinwerktechnik & Messtechnik", Vol. 86, Issue 2, March 1978, pp. 69 to 71 ("Precision Technology and Measuring Technology"), article by R. Arzt and H. Ringelhan, entitled "Optische Sensoren zur beruehrlosen and schlupffreien Weg- und Geschwindigkeits-Messung an Lanfahrzeugen" ("Optical Sensors for Contactless and Slipfree Distance and Speed Measuring of Land Vehicles").
Sensors of this type include an optical system in which a background surface, for example, is imaged over an optical system on a grid. The light flux which is passed by the grid or grating is collected by a field lens on one or two photoelectric transducers or receivers. The temporal course of the resulting electrical signal will then show a modulation in addition to low-frequency changes. The modulation frequency f has an unambiguous relationship with the speed v of the moving object, for example the sensor head.
Arrangements of this type have the disadvantage that the construction is complex and expensive, and requires two optical systems, in which one is located in advance of the grid and the other subsequent to the grid in the image plane. This results in problems during manufacture and in adjustment at a later time. Construction, use, and application, thus, are expensive.